Modern computers utilize a hierarchy of memory devices. To achieve maximum performance levels, modern processors utilize onboard memory and on board cache to obtain high bandwidth access to both program and data. Limitations in process technologies currently prohibit placing a sufficient quantity of onboard memory for most applications. Thus, in order to offer sufficient memory for the operating system(s), application programs, and user data, computers often use various forms of popular off-processor high speed memory including static random access memory (SRAM), synchronous dynamic random access memory (SDRAM), synchronous burst static ram (SBSRAM). Due to the prohibitive cost of the high-speed random access memory, coupled with their power volatility, a third lower level of the hierarchy exists for non-volatile mass storage devices.
Furthermore, mass storage devices offer increased capacity and fairly economical data storage. Mass storage devices (such as a “hard disk”) typically store the operating system of a computer system, as well as applications and data and rapid access to such data is critical to system performance. The data storage and retrieval bandwidth of mass storage devices, however, is typically much less as compared with the bandwidth of other elements of a computing system. Indeed, over the last decade, although computer processor performance has improved by at least a factor of 50, magnetic disk storage performance has only improved by a factor of 5. Consequently, memory storage devices severely limit the performance of consumer, entertainment, office, workstation, servers, and mainframe computers for all disk and memory intensive operations.
The explosion in the data storage market will require both an increase in disk densities as well as a reduction in overall size. This latter aspect, ongoing computer miniaturization will not only affect disk architectures but will create pressure to merge current individual functions into more optimized composite implementations.
The ubiquitous Internet combined with new multimedia applications has put tremendous emphasis on storage volumetric density, storage mass density, storewidth, and power consumption. Specifically, storage density is limited by the number of bits that are encoded in a mass storage device per unit volume. Similarly mass density is defined as storage bits per unit mass. Storewidth is the data rate at which the data may be accessed. There are various ways of categorizing storewidth in terms, several of the more prevalent metrics include sustained continuous storewidth, burst storewidth, and random access storewidth, all typically measured in megabytes/sec. Power consumption is canonically defined in terms of power consumption per bit and may be specified under a number of operating modes including active (while data is being accessed and transmitted) and standby mode. Hence one fairly obvious limitation within the current art is the need for even more volume, mass, and power efficient data storage.
Magnetic disk mass storage devices currently employed in a variety of home, business, and scientific computing applications suffer from significant seek-time access delays along with profound read/write data rate limitations. Currently the fastest available disk drives support only a sustained output data rate in the tens of megabytes per second data rate (MB/sec). This is in stark contrast to the modern Personal Computer's Peripheral Component Interconnect (PCI) Bus's low end 32 bit/33 Mhz input/output capability of 264 MB/sec and the PC's internal local bus capability of 800 MB/sec.
Another problem within the current art is that emergent high performance disk interface standards such as the Small Computer Systems Interface (SCSI-3), Fibre Channel, AT Attachment UltraDMA/66/100, Serial Storage Architecture, and Universal Serial Bus offer only higher data transfer rates through intermediate data buffering in random access memory. These interconnect strategies do not address the fundamental problem that all modern magnetic disk storage devices for the personal computer marketplace are still limited by the same typical physical media restrictions. In practice, faster disk access data rates are only achieved by the high cost solution of simultaneously accessing multiple disk drives with a technique known within the art as data striping and redundant array of independent disks (RAID).
RAID systems often afford the user the benefit of increased data bandwidth for data storage and retrieval. By simultaneously accessing two or more disk drives, data bandwidth may be increased at a maximum rate that is linear and directly proportional to the number of disks employed. Thus another problem with modern data storage systems utilizing RAID systems is that a linear increase in data bandwidth requires a proportional number of added disk storage devices.
Another problem with most modern mass storage devices is their inherent unreliability. Many modern mass storage devices utilize rotating assemblies and other types of electromechanical components that possess failure rates one or more orders of magnitude higher than equivalent solid-state devices. RAID systems employ data redundancy distributed across multiple disks to enhance data storage and retrieval reliability. In the simplest case, data may be explicitly repeated on multiple places on a single disk drive, on multiple places on two or more independent disk drives. More complex techniques are also employed that support various trade-offs between data bandwidth and data reliability.
Standard types of RAID systems currently available include RAID Levels 0, 1, and 5. The configuration selected depends on the goals to be achieved. Specifically data reliability, data validation, data storage/retrieval bandwidth, and cost all play a role in defining the appropriate RAID data storage solution. RAID level 0 entails pure data striping across multiple disk drives. This increases data bandwidth at best linearly with the number of disk drives utilized. Data reliability and validation capability are decreased. A failure of a single drive results in a complete loss of all data. Thus another problem with RAID systems is that low cost improved bandwidth requires a significant decrease in reliability.
RAID Level 1 utilizes disk mirroring where data is duplicated on an independent disk subsystem. Validation of data amongst the two independent drives is possible if the data is simultaneously accessed on both disks and subsequently compared. This tends to decrease data bandwidth from even that of a single comparable disk drive. In systems that offer hot swap capability, the failed drive is removed and a replacement drive is inserted. The data on the failed drive is then copied in the background while the entire system continues to operate in a performance degraded but fully operational mode. Once the data rebuild is complete, normal operation resumes. Hence, another problem with RAID systems is the high cost of increased reliability and associated decrease in performance.
RAID Level 5 employs disk data striping and parity error detection to increase both data bandwidth and reliability simultaneously. A minimum of three disk drives is required for this technique. In the event of a single disk drive failure, that drive may be rebuilt from parity and other data encoded on disk remaining disk drives. In systems that offer hot swap capability, the failed drive is removed and a replacement drive is inserted. The data on the failed drive is then rebuilt in the background while the entire system continues to operate in a performance degraded but fully operational mode. Once the data rebuild is complete, normal operation resumes.
Thus another problem with redundant modern mass storage devices is the degradation of data bandwidth when a storage device fails. Additional problems with bandwidth limitations and reliability similarly occur within the art by all other forms of sequential, pseudo-random, and random access mass storage devices. These and other limitations within the current art are addressed by the present invention.